[libvirt] [PATCH] network: selectively disable -Wcast-align in virNetDevParseDadStatus

[Jim Fehlig]

On 12/02/2015 03:27 AM, Daniel P. Berrange wrote:
> On Tue, Dec 01, 2015 at 05:49:10PM -0700, Jim Fehlig wrote:
>> On 11/30/2015 09:18 PM, Jim Fehlig wrote:
>>> On 11/26/2015 08:10 AM, Ian Campbell wrote:
>>>> Commit 0f7436ca54c9 "network: wait for DAD to finish for bridge IPv6 addresses"
>>>> results in:
>>>>
>>>>  CC     util/libvirt_util_la-virnetdevmacvlan.lo
>>>> util/virnetdev.c: In function 'virNetDevParseDadStatus':
>>>> util/virnetdev.c:1319:188: error: cast increases required alignment of target type [-Werror=cast-align]
>>>> util/virnetdev.c:1332:41: error: cast increases required alignment of target type [-Werror=cast-align]
>>>> util/virnetdev.c:1334:92: error: cast increases required alignment of target type [-Werror=cast-align]
>>>> cc1: all warnings being treated as errors
>>>>
>>>> on at least ARM platforms.
>>> Thanks for looking into this issue Ian.
>>>
>>>> The three macros involved (NLMSG_NEXT, IFA_RTA and RTA_NEXT) all appear to
>>>> correctly take care of alignment, therefore suppress Wcast-align around their
>>>> uses.
>>> Indeed those macros seem to handle alignment, even on one of my older machines
>>> with 2.6 kernel headers. IMO this falls under the "difficult or impossible to
>>> address" scenarios that Daniel mentioned when introducing the VIR_WARNINGS_*
>>> macros via commit e57aaa6f. Adding Daniel to cc for a sanity check of my weak ACK.
>> Looks like I forgot to actually add Daniel to the cc list. Doing so now...
>>
>>> Regards,
>>> Jim
>>>
>>>> Signed-off-by: Ian Campbell <ian.campbell at citrix.com>
>>>> Cc: Maxim Perevedentsev <mperevedentsev at virtuozzo.com>
>>>> Cc: Laine Stump <laine at laine.org>
>>>> Cc: Dario Faggioli <dario.faggioli at citrix.com>
>>>> Cc: Jim Fehlig <jfehlig at suse.com>
>>>> ---
>>>>  src/util/virnetdev.c | 5 +++++
>>>>  1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/src/util/virnetdev.c b/src/util/virnetdev.c
>>>> index ade9afa..0bc809e 100644
>>>> --- a/src/util/virnetdev.c
>>>> +++ b/src/util/virnetdev.c
>>>> @@ -1316,7 +1316,10 @@ virNetDevParseDadStatus(struct nlmsghdr *nlh, int len,
>>>>      struct rtattr *rtattr_ptr;
>>>>      size_t i;
>>>>      struct in6_addr *addr;
>>>> +
>>>> +    VIR_WARNINGS_NO_CAST_ALIGN
>>>>      for (; NLMSG_OK(nlh, len); nlh = NLMSG_NEXT(nlh, len)) {
>>>> +    VIR_WARNINGS_RESET
>>>>          if (NLMSG_PAYLOAD(nlh, 0) < sizeof(struct ifaddrmsg)) {
>>>>              /* Message without payload is the last one. */
>>>>              break;
>>>> @@ -1329,9 +1332,11 @@ virNetDevParseDadStatus(struct nlmsghdr *nlh, int len,
>>>>          }
>>>>  
>>>>          ifaddrmsg_len = IFA_PAYLOAD(nlh);
>>>> +        VIR_WARNINGS_NO_CAST_ALIGN
>>>>          rtattr_ptr = (struct rtattr *) IFA_RTA(ifaddrmsg_ptr);
>>>>          for (; RTA_OK(rtattr_ptr, ifaddrmsg_len);
>>>>              rtattr_ptr = RTA_NEXT(rtattr_ptr, ifaddrmsg_len)) {
>>>> +            VIR_WARNINGS_RESET
>>>>              if (RTA_PAYLOAD(rtattr_ptr) != sizeof(struct in6_addr)) {
>>>>                  /* No address: ignore. */
>>>>                  continue;
>
> Yeah, that looks like about as good as we'll get to deal with this
> so ACK to that change in absence of any better suggestion.

Thanks. I noticed DV tagged 1.3.0-rc1, but I've pushed this since it fixes build
failures on some arch.

Regards,
Jim